Automatic injection devices offer an alternative to manually-operated syringes for administering therapeutic agents into patients' bodies and allowing patients to self-administer therapeutic agents. Automatic injection devices may be used to administer medications under emergency conditions, for example, to administer epinephrine to counteract the effects of a severe allergic reaction. Automatic injection devices have also been described for use in administering anti-arrhythmic medications and selective thrombolytic agents during a heart attack. See, for example, U.S. Pat. Nos. 3,910,260; 4,004,577; 4,689,042; 4,755,169; and 4,795,433, the entire contents of which are incorporated herein in their entirety by reference. Various types of automatic injection devices are also described in, for example, U.S. Pat. Nos. 3,941,130; 4,261,358; 5,085,642; 5,092,843; 5,102,393; 5,267,963; 6,149,626; 6,270,479; and 6,371,939; and International Patent Publication No. WO/2008/005315, the entire contents of which are incorporated herein in their entirety by reference.
Conventionally, an automatic injection device houses a syringe and, when operated, causes the syringe to move forwardly and a needle to project from the housing so that a therapeutic agent contained in the syringe is injected into a patient's body.
A conventional automatic injection may include one or more needle shields to protect the syringe needle from damage and accidental contact and to maintain sterility of the injection needle. Needle shields include a soft needle shield that is formed of a flexible material, and a rigid needle shield that is formed of a rigid, inflexible material and that provide greater mechanical protection to the injection needle. Conventional automatic injection devices may also include a removable cap covering the needle shields to provide mechanical protection for the needle shields and to facilitate removal of the needle shields before an injection may be performed.
FIGS. 1A and 1B illustrate an exemplary syringe 100 including a substantially tubular syringe body 102 for holding a therapeutic agent. FIG. 1A illustrates a side view of the exemplary syringe 100. FIG. 1B illustrates a cross-sectional view of the exemplary syringe 100 bisected along the longitudinal axis L. An injection needle may be coupled at a distal end of the syringe body 102. The injection needle may be covered and protected by a soft needle shield 104 and a rigid needle shield 106 that surrounds the soft needle shield 104. One or more apertures 108 may be provided in a side wall of the rigid needle shield 106 to allow a portion of the soft needle shield 104 to extend through the apertures 108. This permits the soft needle shield 104 and the rigid needle shield 106 to latch together which, in turn, permits removal of both the soft needle shield 104 and the rigid needle shield 106 when the rigid needle shield 106 is pulled away from the syringe body 102 in the distal direction (represented by arrow R), thereby exposing the injection needle for use in performing an injection. In an exemplary embodiment, a ridged portion 110 may be provided in the exterior surface of the rigid needle shield 106. The ridged portion 110 may include one or more alternating outwardly-projecting ridges interspaced with grooves, and may thereby provide a region of higher friction contact for removal of the rigid needle shield 106 from the syringe.